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Re: [libvirt] [RFC]: Snapshot API



On Wed, Mar 24, 2010 at 02:42:30PM +0100, Matthias Bolte wrote:
> 2010/3/24 Daniel P. Berrange <berrange redhat com>:
> > On Wed, Mar 24, 2010 at 09:09:08AM -0400, Chris Lalancette wrote:
> >> On 03/24/2010 04:52 AM, Paolo Bonzini wrote:
> >>
> >> >
> >> >> > How can<parent>  be settable? If I have snapshots A and B
> >> >> >
> >> >> >    A ->  B ->  current state
> >> >> >
> >> >> > and I create a new snapshot C, then B will be the parent of C.
> >> >> >
> >> >> >    A ->  B ->  C ->  current state
> >> >> >
> >> >> > If I create another snapshot D now and specify A to be its parent,
> >> >> > what's supposed to happen then?
> >> >>
> >> >> You are right, that doesn't make that much sense.  I have to admit that
> >> >> the tree structure is the part I thought about least, so I'll take that
> >> >> part back. <parent> is just going to be an informational field about
> >> >> which snapshot was current (if any) when this one was created.
> >> >
> >> > If discarding a snapshot also discards the children, it would definitely
> >> > make sense to be able to specify the parent.
> >>
> >> The problem, though, is what Mattias points out; there is no (easy) way
> >> that, given state C, I can get back to state A to make a new snapshot.
> >> I actually have to be at state A to take a new snapshot with a parent of
> >> A.  I think this is a place where we have to make it manual; if you really
> >> want a new snapshot that is a child of A, you'll have to manually shutdown
> >> your domain, boot to snapshot A, then take a snapshot of A.
> >
> > This is something virDomainCreateAtSnapshot() should solve.
> >
> > If you have a series
> >
> >   A -> B -> C
> >
> > And you do  virDomainCreateAtSnapshot(dom, "A"), then you get 'D'
> >
> >   A -> B -> C
> >   |
> >   \-> D
> 
> You mean you get D when you do a virDomainSnapshotCreateXML(dom, NULL)
> _after_ you've done a virDomainCreateAtSnapshot(dom, "A"), don't you?

Well I'll have to look up what VMWare does really, since their behaviour
is what I intended

Daniel
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